This invention relates to the treatment of drill cuttings contaminated with oil for environmentally acceptable disposal, and more particularly to sequential treatment of the drill cuttings with an optional organic demulsifier, an acidification agent and alkaline earth for the purpose of rapidly removing the oil from the drill cuttings to obtain treated drill cuttings essentially free of oil.
Oil-based drill cuttings are generally regarded as controlled or hazardous waste. As such, the drill cuttings can be disposed of in two different ways: (1) decontamination treatment; or (2) hazardous waste controlled landfill. Hazardous waste is considered a threat to the environment due to the risk of surface and subsurface water pollution, as well as air pollution, interrupting the equilibrium of the ecosystem. The disposal of hazardous waste in controlled landfills is usually the last environmental option, since the problem is only transferred from one place to another and the ultimate solution is merely postponed for a later date.
There are several technologies available to treat hazardous wastes by different means. All of them have advantages and limitations depending upon the contaminant type and concentration, the matrix in which the contaminant is dispersed, and finally the locations at which the cuttings are generated and are to be disposed of, which can be the same or different. The handling and treatment costs, process time, contaminant locations such as ecologically protected areas, nearby water bodies, human residences, desert, etc. and finally the total treatment time, are all factors in selecting the best available technology.
Oil and gas exploration depend on drilling wells at different depths with different diameters throughout different geological strata with multiple lithological manifestations such as clay, rock, sand, empty underground salt mines, brine and water tables. Drilling requires a drilling fluid, also known as drilling mud, with various physical functions such as: (1) Cooling and lubrication of the drill bit; (2) Formation of a filter cake for temporarily xe2x80x9ccasingxe2x80x9d the wellbore; (3) Carrying the drill cuttings from the bit to the surface; and (4) Preventing blowout of reservoir fluids. The solid pieces of material cut by the bit, as the drilling advances, are known as drill cuttings. The drilling mud is a fluid of physical-chemical compounds with specific rheological characteristics to cover all the needs of the well as the different geological layers, depths and extreme pressure of natural fluids are met. There are two principal types of mud: (1) Oil-based mud (also known as inverse emulsion mud); and (2) Water-based mud. Their formulations vary according to the technology of each supplier and the general characteristics of each well in each field. These formulations are generally expensive, which is the reason for recirculating them. Before recirculation, their formulation must be adjusted to replace compounds lost during the process. The composition of many drilling muds typically includes the following compounds: (1) Bentonite; (2) Barite; (3) Diesel or other oil; (4) Polymers; (5) Sodium and potassium chlorides; and (6) Water. Water-based mud does not use diesel or oil but does use the chlorides; the inverse emulsion uses more diesel than water. As used herein, the term xe2x80x9coil-based mud xe2x80x9d also includes synthetic muds that are sometimes classified separately even though they contain appreciable amounts of hydrocarbons, usually refined hydrocarbons instead of diesel. Because they do not contain difficult-to-dispose-of oil, water-based mud is sometimes used instead of the oil-based drilling fluids, even though the oil-based muds can be cheaper to use and can have operating advantages.
It is important to remember that, in all cases, the mud is a stable physical emulsion, necessarily so in order to prevent separation of its components that have different densities and other physical-electrical characteristics. Mud can be sticky and elastic, like gum, without losing its fluid qualities. As the contaminated oil-based drill cuttings lose water, they become stickier.
The mud is injected through the center of the drill string to the bit and exits to the surface in the annulus between the drill string and the wellbore, fulfilling, in this manner, the cooling functions and lubrication of the bit, casing of the well and, finally, carrying the drill cuttings to the surface. At the surface, the mud is separated from the drill cuttings to be reused, and the drill cuttings are disposed of, usually in controlled landfills.
The separation of the mud and drill cuttings is not perfect since the cuttings retain part of the drilling mud in concentrations that vary between 25 and in excess of 50 weight percent. Thus, drill cuttings can be considered hazardous waste, depending on the residual components of the mud and their concentrations. Environmental concerns demand that the drill cuttings showing contaminant characteristics, because of hazardous compound concentrations such as diesel, chlorides, polymers, etc., be handled and processed carefully before disposal into the environment. The best known prior art technologies for the treatment of inverse emulsion contaminated drill cuttings are: (1) Incineration; (2) Stabilization and Encapsulation; (3) Thermal Desorption; (4) Chemical Oxidation; (5) Biochemical Degradation; and (6) Controlled Landfills. The criteria used most often for selecting the best technology are: (1) Environmental reliability (environmental risk); (2) Specific environmental requirements, by legislation as well as geographical location; (3) Limitations presented by each technology (reliability of the equipment and processes); (4) Costs; (5) Process speed vs. cuttings generation speed; (6) Available space for treatment; (7) Characteristics of the final disposal site; and (8) Logistics. Encapsulation is seldom used because of the high risks involved since there is no guarantee of 100% encapsulation nor is there a guarantee that encapsulation will last over a long period of time under any environment at the final disposal site. Examples of encapsulation are seen in U.S. Pat. No. 4,913,586 to Gabbita; and U.S. Pat. No. 5,630,785 to Pridemore et al.
Biochemical degradation, as in U.S. Pat. No. 5,039,415 to Smith, requires constant supervision and control during the entire process, and this option is very slow and might take several years for treatment in each case. Controlled landfill is less and less attractive since the problem is not solved, and only changes the place and time for ultimate resolution.
Examples of incineration processes include U.S. Pat. No. 1,444,794 to Kernan; and U.S. Pat. No. 4,606,283 to DesOrmeaux et al. The main limitation for incineration lies in its operational costs, and the process control is also difficult since the tight stoichiometric operating ranges are hard to maintain when, in practice, contaminant concentrations are often variable. Moreover, the incineration process is energy intense because the entire matrix has to be heated to combustion temperatures, many constituents of which have high thermal coefficients. Furthermore, flexibility to set up incineration equipment in the field is low and the logistical costs are high.
Thermal desorption, as in U.S. Pat. Nos. 5,228,804 to Balch, 5,272,833 to Prill et al. and/or 5,927,970 to Pate et al., presents several limitations, including low thermal efficiency, poor process control, low flexibility, high investment cost, high operating cost, and low feasibility for in situ projects. The thermal efficiency of thermal desorption is even lower than incineration since the heating of the entire matrix has to be indirect, creating additional investment, maintenance and operational costs, with poor process control. The viscoelastic characteristics of the drill cuttings make processing difficult because of the tendency for the drill cuttings to stick to walls and other equipment surfaces, thus reducing the thermal transmission by effectively decreasing the inner diameter of the drum with less productivity and/or quality. Furthermore, thermal desorption requires additional treatment for the recovered gases, by condensation or other means of treatment, further increasing its cost.
Chemical oxidation is disclosed in U.S. Pat. No. 5,414,207 to Ritter, for example. In this approach, lime preconditioned with a hydrophobizing agent is blended with wet soil in an inert atmosphere and introduced to a decomposition vessel. Air is then introduced to the mixture to effect oxidation and/or hydrolysis of the oil contaminants. The main focus of this approach is to delay hydrolysis of the lime until well after the mixture is blended to favor oxidation/hydrolysis of the organic contaminants, and as a consequence the process is relatively slow and not continuous.
The present invention is the discovery of a chemical oxidation/desorption method and system for treating drill cuttings for environmental disposal. Where necessary, the process pretreats the drill cuttings with an emulsion breaker, followed by mixing with a mineral acid, and then mixes the acidified cuttings with alkaline earth, preferably under conditions of high shear. The process steps are strongly exothermic and generate gaseous products to quickly remove the oil from the drill cuttings, e.g. in a residence time of approximately 60-80 seconds. The present invention thus achieves very rapid and extensive oil removal, reliability, efficiency and low costs with minimal energy consumption.
In one embodiment, the present invention provides a method particularly well-suited for treating a substrate comprising oil-contaminated clay for disposal. The method includes admixing the substrate with a concentrated mineral acid under high shear conditions to obtain a pre-heated, acidified admixture having an aqueous phase with a pH less than 0. The resulting admixture is admixed with alkaline earth under high shear conditions in an amount effective to generate an exotherm to vaporize the oil and reaction products thereof. A solid reaction product is recovered that is essentially free of oil. If necessary or desired, the substrate can be comminuted prior to the admixture with the mineral acid. Optionally, the substrate can be pretreated with an organic emulsion breaker prior to the admixing with the mineral acid. The substrate preferably comprises drill cuttings, although the method can also be used to remove hydrocarbons from a wide variety of substrates, particularly substrates containing clay. The method is especially attractive for treating drill cuttings contaminated with oil-based drilling mud.
Where the emulsion breaker is used in the method, it is preferably an organic acid or addition salt, such as, for example, alkylsulfonate, arylsulfonate, alkylarylsulfonate, aralkylsulfonate, or a combination thereof, more preferably alkylsulfonic acid, arylsulfonic acid, alkylarylsulfonic acid, aralkylsulfonic acid, or a combination thereof. In a particularly preferred embodiment, the organic acid or addition salt comprises aqueous alkylbenzenesulfonate, for example, alkylbenzenesulfonic acid, and especially dodecylbenzenesulfonate, e.g. dodecylbenzenesulfonic acid (DDBSA). The emulsion breaker is preferably admixed at a rate of from 0.5 to 5 parts by weight per 100 parts of substrate, more preferably at from 1 to 3 parts, and especially at from 1 to 1.5 parts.
The mineral acid is preferably sulfuric acid. The mineral acid is preferably admixed at a rate of from 1 to 20 parts by weight per 100 parts of substrate, more preferably from 2 to 13 parts by weight, and especially from 4 to 7 parts by weight. If desired, a proportion of water can be added with the substrate and mineral acid at a total rate from 20 to 40 parts by weight per 100 parts of the substrate.
The alkaline earth is preferably lime. The lime is preferably admixed in a proportion of from 1 to 16 parts by weight per 100 parts of the substrate, more preferably from 2 to 10 parts, and especially from 3 to 6 parts by weight.
The mineral acid admixing is preferably performed in a first reactor, and admixing the alkaline earth is performed in a second reactor receiving the admixture discharged from the first reactor. The emulsion breaker and the mineral acid admixing can be performed serially in a first reactor. The method preferably includes recovering vapor generated from the first and second reactors, condensing the recovered vapor and exhausting non-condensed gases.
In another embodiment, the present invention provides a method for treating drill cuttings contaminated with oil. The method includes: (a) continuously introducing the drill cuttings into an inlet end of a first reactor comprising at least one rotatable shaft disposed longitudinally in a housing and a plurality of impellors spaced along the shaft; (b) if the drill cuttings have a water content of less than 20 weight percent or an oil content of more than 30 weight percent, continuously introducing an aqueous organic emulsion breaker into the first reactor at a first location adjacent the inlet end; (c) continuously introducing a mineral acid into the first reactor at a second location spaced from an outlet end of the first reactor; (d) rotating the at least one shaft of the first reactor to continuously maintain high shear conditions in the first reactor and discharge an acidified intermediate product; (e) continuously introducing the acidified intermediate product into an inlet end of a second reactor comprising at least one shaft disposed longitudinally in a housing and a plurality of impellors spaced along the shaft; (f) continuously introducing alkaline earth into the second reactor at a location adjacent the inlet end thereof; (g) rotating the at least one shaft of the second reactor to maintain high shear conditions in the second reactor and continuously discharge a reaction product from the outlet end of the second reactor, wherein the reaction product is essentially free of oil.
The proportion of water added to the first reactor with any emulsion breaker and the mineral acid preferably totals from 0 to 40 parts by weight per 100 parts of the drill cuttings. The method can also include recovering vapor generated from the first and second reactors, scrubbing the recovered vapor and exhausting non-condensed gases from the recovered vapor into the atmosphere.
In another embodiment, the present invention provides a method for treating drill cuttings contaminated with oil, comprising: (a) continuously introducing the drill cuttings into an inlet end of a first reactor comprising at least one rotatable shaft disposed longitudinally in a housing and a plurality of impellors spaced along the shaft; (b) continuously introducing from 1 to 3 parts by weight per 100 parts drill cuttings of dodecylbenzenesulfonic acid into the first reactor at a first location adjacent the inlet end; (c) continuously introducing from 2 to 13 parts by weight per 100 parts drill cuttings of sulfuric acid into the first reactor downstream from the first location; (d) rotating the at least one shaft of the first reactor to continuously maintain high shear conditions in the first reactor and discharge an acidified intermediate product; (e) continuously introducing the acidified intermediate product into an inlet end of a second reactor comprising at least one shaft disposed longitudinally in a housing and a plurality of impellors spaced along the shaft; (f) continuously introducing from 2 to 10 parts by weight per 100 parts drill cuttings of lime into the second reactor at a location adjacent the inlet end thereof; (g) rotating the at least one shaft of the second reactor to maintain high shear conditions in the second reactor and continuously discharge a reaction product from the outlet end of the second reactor, wherein the reaction product contains less than 3000 ppm oil; (h) recovering vapor from the first and second reactors; (i) condensing liquid from the recovered vapor to form an exhaust stream of uncondensed vapor.
In a further embodiment, the present invention provides an apparatus for treating a substrate comprising oil-contaminated clay particles for disposal. The apparatus includes first means for admixing the substrate with a concentrated mineral acid under high shear conditions to obtain a pre-heated, acidified admixture having an aqueous phase with a pH less than 0, second means for admixing the admixture from the first means with alkaline earth under high shear conditions in an amount effective to generate an exotherm to vaporize the oil and reaction products thereof, and means for recovering a substantially solid reaction product from said third means essentially free of oil.
In a further embodiment, the present invention provides apparatus for treating drill cuttings contaminated with oil. The apparatus includes means for continuously introducing the drill cuttings into an inlet end of a first reactor comprising at least one rotatable shaft disposed longitudinally in a housing and a plurality of impellers spaced along the shaft, means for continuously introducing an aqueous emulsion breaker into the first reactor at a first location adjacent the inlet end, means for continuously introducing a mineral acid into the first reactor at a second location spaced from an outlet end of the first reactor, means for rotating the at least one shaft of the first reactor to continuously maintain high shear conditions in the first reactor and discharge an acidified intermediate product, means for continuously introducing the acidified intermediate product into an inlet end of a second reactor comprising at least one shaft disposed longitudinally in a housing and a plurality of impellers spaced along the shaft, means for continuously introducing alkaline earth into the second reactor at a location adjacent the inlet end thereof, and means for rotating the at least one shaft of the second reactor to maintain high shear conditions in the second reactor to continuously discharge a reaction product from the outlet end of the second reactor essentially free of oil.
In an alternate embodiment, the present invention provides an apparatus for treating drill cuttings contaminated with oil. The apparatus includes a first reactor comprising a longitudinal housing having an inlet at a first end and an outlet at an opposite end, at least one rotatable shaft disposed longitudinally in the housing, and a plurality of impellers spaced along the at least one shaft, and a second reactor comprising a longitudinal housing having an inlet at a first end and an outlet at an opposite end, at least one rotatable shaft disposed longitudinally in the housing, and a plurality of impellers spaced along the at least one shaft. A first solids feeder is provided for continuously introducing drill cuttings into the inlet of the first reactor. The apparatus includes a tank of emulsion breaker and a line from the emulsion breaker tank for continuously introducing the emulsion breaker into the first reactor adjacent to the inlet. There is a tank of aqueous mineral acid and a line from the mineral acid tank for continuously introducing the mineral acid into the first reactor downstream from the emulsion breaker and upstream from the outlet. A chute is provided for continuously transferring reaction product from the outlet of the first reactor into the inlet of the second reactor. A second feeder is provided for continuously introducing alkaline earth into the second reactor adjacent the inlet end. A third feeder continuously moves reaction product away from the outlet of the second reactor. The apparatus further includes a vapor collection system for recovering gases from the first and second reactors, a condenser for condensing liquid from the gases from the vapor collection system and producing a stream of uncondensed gases, and an exhaust port for discharging uncondensed gases.
The first and second solids feeders preferably include a vapor lock for inhibiting passage of gases from the respective reactors. The emulsion breaker tank can include a charge of dodecylbenzenesulfonic acid. The mineral acid tank can include a charge of sulfuric acid. The apparatus can also include a water line for introducing water with the emulsion breaker and/or mineral acid.
An alkaline earth hopper can be provided for supplying alkaline earth to the second feeder. The alkaline earth hopper can include a charge of lime.
The apparatus preferably includes controllers for metering the rates of the emulsion breaker, mineral acid and lime proportional to a rate of the drill cuttings introduction.
The condenser can include an indirect heat exchanger for cooling the gases, or a direct heat exchanger for contacting the gases with a liquid absorption medium.
Another embodiment of the invention provides a system for drilling a subterranean well with the circulation of oil-based mud without discharging oil-contaminated drill cuttings. The system includes a drilling rig having a drill string for drilling the well and a mud circulation system for circulating oil-based mud and recovering drill cuttings, and a drill cutting treatment unit operatively associated with the drilling rig for receiving the recovered drill cuttings and producing treated drill cuttings of reduced oil content. The treatment unit preferably comprises the apparatus described above.
A further embodiment of the invention provides a method for drilling a subterranean well with the circulation of oil-based mud without discharging oil-contaminated drill cuttings. The method includes operating a drilling rig including a rotary drill string to drill the well, circulating oil-based mud through the drill string to remove drill cuttings from the well, recovering the drill cuttings from the mud, and treating the drill cuttings according to the method described above.